I was driving normally on the road that day. The brake pedal suddenly can’t be pressed down. Fortunately, the brake returned to normal to slow the speed down when I pressed the brake pedal again after a while. I am still so scared as soon as recalling this experience! Why is it so happened?
There is an important component in the hydraulic brake system of many vehicles, namely the vacuum booster, which is installed between the brake pedal and the brake master cylinder, and acts as a booster to increase the power applied to the master cylinder when the driver is pressing down on the brake pedal. If brake stiffness is due to a fault, usually it is the vacuum booster and related components that have failed. Now let's see how the vacuum booster works and how to detect and repair such failures.
How the vacuum booster works
When the engine is working, it will inhale air. A vacuum is generated on one side of the vacuum brake booster diaphragm by means of a vacuum pipe connected to the engine air intake system, while the other side is the normal air pressure, thus creating a pressure difference that increases the thrust applied by the brake pedal to the brake master cylinder. So when we press the brake pedal, it feels like we can stop the vehicle with a light pressure on the brake pedal.
Vacuum booster troubleshooting
Based on the working principle of the vacuum booster, the vacuum booster will work only if the engine is working. When the engine is turned off, the vacuum in the vacuum booster will gradually disappear, so the brake pedal can be pressed down right after the engine is turned off, but becomes difficult to be pressed down after a few times because the vacuum has disappeared. At this point, the hydraulic brake system is not malfunctioning, but is unable to stop the vehicle by just pressing the brake pedal with normal force given the vacuum loss.
If the brake pedal becomes stiff after being pressed a few times when the engine is turned off; and becomes soft and depresses after being pressed when the engine is started, then the vacuum booster is working. At this point one should continue to check the vacuum pipe for leakage that can result in insufficient engine vacuum. If the vacuum pipe leaks, it will usually affect the engine’s idle speed, which will cause the engine to shut down in the event of unstable idle speed or when idle.
If the vacuum pipe and the one-way valve connected to the booster are trouble free, and the fault is occasional, then the vacuum booster is usually faulty and should be replaced.
If carbon deposits clog the engine vacuum pipe or cause the nozzle to become smaller, the vacuum booster may not have enough vacuum, so that it feels stiffer and stiffer when the brake is pressed consecutively, but feels normal when the brake is pressed again after a long time.
In high altitude regions, if the foot is constantly pressed on the brake pedal, the vacuum booster may not have enough vacuum, so that it feels stiff when the brake is pressed.
Nothing is unimportant in brake system failure. Only through regular vehicle inspection and maintenance the chance of brake system failure be reduced, ensuring driving safety.
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